A technology is known wherein an molded article having a required shape is molded by heat, compression molding using a fiber-reinforced resin molding material comprising bundled aggregates (hereinafter, also referred to as fiber bundles) of discontinuous reinforcing fibers (for example, carbon fibers) and matrix resin (for example, a thermosetting resin) in, for example, JP-A-2013-202890, JP-A-2008-174605, JP-A-2009-191116, JP-A-2010-163536 and WO 2014/021315. In such a conventional fiber-reinforced resin molding material, when the fiber bundle in the fiber-reinforced resin molding material comprises a fiber bundle with a certain number of single fibers formed from a predetermined strand, in a molding material comprising fiber bundles with a large number of single fibers, although the flowability during molding is excellent, the mechanical properties of a molded article tend to be poor.
For example, JP '890 discloses a molding material in which the number of filaments of a chopped fiber bundle in the molding material is 10,000-700,000. In such a molding material, although a large number of filaments of the fiber bundle reinforcing fibers can efficiently move together with the resin as a fiber bundle at the time of molding and, therefore, an excellent flowability can be obtained, with respect to a molded article due to this molding material after molding, there is a high possibility to cause stress concentration at the end portion of the fiber bundle or the like in the molded article when the molded article is broken, and it is not suitable for molding a molded article required with high mechanical properties.
On the other hand, for example, in JP '605, although a fiber-reinforced resin is disclosed which uses fiber bundles dispersed so that the number of single fibers becomes 100 or less because the number of single fibers is small compared to the formation disclosed in JP '890, the reinforcing fibers well disperse in the molded article, the possibility to cause stress concentration at the end portion of the fiber bundle or the like in the molded article becomes low and the mechanical properties of the molded article can be enhanced and, on the contrary, there remains a possibility that a high flowability at the time of molding as expected cannot be obtained.
As described above, in a fiber-reinforced resin molding material using fiber bundles with a relatively large number of single fibers, although production efficiency is good and excellent flowability at the time of molding tends to be obtained, the mechanical properties of a molded article tend to be poor and, in a fiber-reinforced resin molding material using fiber bundles with a relatively small number of single fibers, on the contrary, although the mechanical properties of a molded article are excellent, flowability at the time of molding tends to be difficult to be enhanced.
Accordingly, paying attention to the tendencies in the above-described conventional technologies, it could be helpful to provide a fiber-reinforced resin molding material capable of achieving at a good balance both good flowability during molding and excellent mechanical properties of a molded article, and a production method thereof.